BOSTON/HOPKINTON, April 21 (Reuters) - Nearly 36,000 athletes will run in the 118th Boston Marathon on Monday in the first running of the race since last year's bombing, with top-ranked Kenyan and Ethiopian runners among the second-largest field in the race's history.

Racers faced new security restrictions at the event, a reaction to the attack that killed three people and injured 264 when, authorities say, two ethnic Chechen brothers dropped homemade explosives in backpacks at the finish line.

Thousands of runners gathered at a park in downtown Boston before the race, preparing to board buses that would take them to the race's start line in Hopkinton, 26.2 miles west of Boston.

Track coach Robert Hollis, who had traveled from New Jersey for the race, admitted to some security worries.

"There is some nervousness. I wasn't scared until 15 minutes ago, but when I saw all those cops and the dogs on the Amtrak train, I got a little nervous," he said. "We just live in a different age and time now."

Race organizers said 35,755 runners gathered in Hopkinton, where police were out in force and helicopters hovered overhead, for their start times.

"I came a long way for this," said 26-year-old John Finn, who had traveled from Berkeley, California, to run. "I was hoping to get into the marathon even before the bombing. But after it happened last year, I knew that this was something I wanted to be a part of, that it would be special."

Among the top-ranked runners, returning men's and women's champions Lelisa Desisa of Ethiopia and Rita Jeptoo are set to run this year's race.

Each faces a rival with a faster personal-best time: Dennis Kimetto of Kenya ran last year's Chicago Marathon in 2:03:45 and Ethiopia's Mare Dibaba turned in a 2:19:52 performance at the 2012 Dubai marathon.

No American athlete has stood atop the podium on Boston's Boylston Street, not far from the site of last year's bombing, since 1985 when Lisa Larsen-Weidenbach of Michigan won the women's race. The drought has been longer for U.S. men: Greg Meyer of Massachusetts won in 1983.

But there are several U.S. hopefuls in the field, including Ryan Hall of California, who placed third in 2009 and Desiree Linden, who missed winning by just two seconds in 2011.

Race organizers expanded the field by some 9,000 runners this year, to allow the roughly 5,000 athletes who had been left on the course last year when the twin pressure-cooker bombs went off near the finish line another chance to compete.

Amateur runners often work for years to post the strict age-graded times needed to qualify for the elite race. (Reporting by Scott Malone; Editing by Bernard Orr and Sofina Mirza-Reid)

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